Calcium-cyanide product



Patented Dec. 13, 1927.

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ROBERT W. POINDEXTER, JR, 0! LOS ANGELES, CALIFORNIA, ASSIGNOR TOCALIFOR- NIA CYANIDE COMPANY, INGOR'IPORATEEOF NEW YORK, N. Y., ACDBPORATION OF DELAWARE.

No Drawing;

This invention relates to' a process of producing'normal calcium cyanideand to the product thereof. This product is a dry solid material whichis adapted for a variety of'uses and is particularly available as asource of hydrocyanic acid because it decomposes readily when exposed toa moist atmosphere.

Chemical literature contains numerous statements to the effect thatcalcium cyanide cannot be prepared in a solid and substantially pureformi Calcium cyanide can be prepared in solution by adding hydrocyanicacid to a suspension of calcium hydroxide but the cyanide'decomposeswhen such solutions are evaporated. It has been discovered recently byMetzger that calcium cyanide having combined hydrocyanic acid can beproduced by subjecting. calcium carbide to the action of hydrocyanicacid. I have describedin acopending Patent No. 1,596,120 a method ofpreparing calcium cyanide containing combined ammonia; The product ofthe recess described herein differs'from the pro u'cts mentioned in thatit contains no appreciable amount of combined hydrocyanic acidor'ammonia. It is substantially the normal calcium cyanide Ca(CN-) Theproduct is similar in many respects to the calcium cyanide productscontaining com bined hydrocyanic acidor ammonia. It is, however,adistinct chemical compound and consequently some of itsproperties aredifferent from those of the earlier products.

It is the object of the present invention.

to provide a process of preparing a dry substantially pure and solidcyanide of calcium and a product having substantially the compositionindicated by the forinula Ca (CN) Otherobjects and advantages of theyin- V vention will be apparent as it is better understood by referenceto the following specification. I

In carrying out the invention I follow preferably the procedure asindicated in my copending application above identified for theproduction of calcium cyanide with com- 1 bined" ammoma; I havediscovered that when the preduct of this process is heated.

Application filed. April 13, 1926 Serial N01 101 832.

under regulated conditions the ammonia can be substantially removed fromthe com. pound, leaving calcium cyanide as the product. In order tosecure the desired re sult the calcium cyanide containing combinedammonia should be reasonably pure and as free as possible from water. Itshould be free also from calcium nitrate or other calcium salts whichhave been used in the preparation of the ammonia-containing' cyanide;Freedom from water can be attained by the use of substantially anhydrousliquid ammonia in the preparation of the ammonia containing cyanide.That product can be freed from deleterious salts by sufiicient washingwith anhydrous liquid ammonia. v

The separation of the ammonia from the ammonia-containing cyanide isaccomplish'ed by heating the cyanide in a partial vacuum-to atemperature which should not.

exceed 325 C. The vacuum is used to avoid the contact of air andparticularly moisture with the material since it decomposes readily inthe presence of moisture and to facilitate the removal of the evolvedammonia. The treatment should be continued until substantially all ofthe ammonia has been removed. The product, which is pure calcium cyanidein a dry and solid form, should then be promptly sealed in suitablepackages to prevent access of the atmosphere and moisture thereto.

' The preparation of the ammonia-contain ing cyanide can be conducted invarious ways. As indicated in the application above referred to, thepreferred process is to dissolve a suitable salt of calcium such ascalcium nitrate in anhydrous liquid ammonia. To this may be added eitherhy-' drocyanic acidor a solution of ammonium cyanide in anhydrous liquidammonia. Any other cyanide which is s'oluable in the liquid ammonia canbe substituted for ammonium cyanide or hydrocyanic acid. lVhe'nhydrocyanic acid is added to anhydrous liquid ammonia or to a solutionof a suitable salt in the liquid ammonia, ammonium cyanide formedapparently and may be considered as the reacting cyanogen salt. Theoperatlon may be conducted satisfactorily by preparing two solutions,one consisting of the calcium salt dissolved in anhydrous liquid ammoniaand the other consisting of anhydrous liquid ammonia to whichhydrocyanic acid has been adoed. lVhen the two solutions are combined adouble decom position occurs and a precipitate is formed. Theprecipitate can be filtered from the solution. It should be washedthoroughly with anhydrous liquid ammonia to remove all traces of othercalcium salts.

It is not essential that the ammonia used as a solvent be strictlvanhydrous l have experienced no ditlici ty in using ammonia whichcontained a -nall amount of water. Likewise, it is possible to employcalcium salts which contain water of crystallization. This waterliberated during the reaction but does not interfere v th the productionof the cyanide. As hereinbefore indicated,

however, the amount of water should be reduced to a minimum and watershould be absent preferably if the ammonia-containing cyanide is to beSlllDjQCtQClliO further treatment for the removal of the ammonia.

In carrying out the process the acid radical of the salt used combineswith ammonia in the mother liquor. Thus, if calcium nitrate is used theliquor contains ammonium nitrate. The liquor can be evaporated torecover the free a nmonia and to deposit the ammonium salt, for example,ammonium nitrate. This salt can be utilized as a byproduct forfertilizing or other uses. It can be decomposed also by the addition ofcalcium oxide or hydroxide to regenerate the ammonia and the calciumsalt, for example, calcium nitrate Both of these products can bereturned to the process, thus providing a cyclic operation in which allof the materials entering the reaction are withdrawn either as thecyanide product or reused to generate that product.

To obtain the calcium cyanide substantially free from ammonia theammonia-conraining cyanide having the composition, for

example, Ca(CN) QNH should be subjected in a suitable closed receptacleto a partial vacuum produced by a vacuum pump and heated at the sametime until the ammonia is evolved freely. The heating should becarefully controlled so that it does not at any time exceed 325 C. andshould be continued until substantially all of the ammonia has beenseparated. The end point can be determined by analysis of samples takenfrom time to time. WVhen the separation is complete the cyanide shouldbe cooled and placed promptly in suitable sealed receptacles.

Any convenient form of apparatus may be employed in carrying out theoperation. For example, a vacuum shelf dryer of any type may be employedif means for heating the shelves to the requisite temperature isavailable. It is important in carrying out the operation that air beexcluded, be-

cause of the tendency of the material to decompose particularly in thepresence of moist air. Consequently the cyanide precipitate containingammonia should be transferred as promptly as possible to the drier inwhich the removal of ammonia is ac ('oniiplished.

As an example of the application of the process, I placed about 1.50 c.c. of commercial anhydrous liquid an'imonia in a Dewar test tube andadded c. c. of hydrocyanic acid. thus forming a solution of ammoniumcyanide. In another Dewar test tube 10 grams of calcium nitrate Ca(NO.4H O were dissolved in about 100 c. c, of commercial anhydrous liquidammonia. monium cyanide solution was then added to he calcium nitratesolution until precipitation ceased. The precipitate was filtered withthe aid of suction and washed with c. c. of anhydrous liquid ammonia.The precipitate was then placed in a 150 c. c. Erlenmeyer flask andl'ieated under28 inches of vacuum to :1 temperature somewhat below 325C. The drying temperature was controlled by supporting the flask in anair bath.

Several batches of the product were made in the manner indicated andthree of them showed the following analyses:

These analyses indicate that the roduct approximates normal calciumcyani e Ca(CN) 2 but that a relatively small amount of cyanogen has beenevolved with the ammonia resulting in the production of a slightlybasicsalt. Better control of the conditions during the removal of the ammoniawill undoubtedly permit the production of a strictly normal salt.

The product is very soluble in water, forming a faintly yellow solution.There is a small amount of insoluble lime in the solution which probablyrepresents the excess of lime from which the cyanogen has been evolved.The compound is moderately soluble in methyl alcohol but after a certainconcentration is reached the material is decomposed with precipitationof calcium hydroxide.

When the product is exposed to the atmosphere hydrocyanic acid isreadily evolved. If ignited the hydrocyanic acid burns with considerablevolume of flame. The following table shows the result of an evolutionThe amtest made on layers one-eighth of an inch in depth:

Temperature 65 F.

Relative humidity 80%.

'The material when pine is nearly white and When kept from theatmosphere the color does not change appreciably. It is a very finelydivided light powder. It loses very little of its cyanogen bydecomposition unless exposed to the atmosphere. After three Weeks thecolor of the compound became a very light yellow but the change was notdistinguishable except by a comparison of a sample with freshly preparedmaterial. The fact that the color did not alter after exposure to theatmosphere together with the fact that the alkaline solutions of theevolution test residues were practically colorless when filteredindicates that substantially all of the contained cyanogen is availableas HCN and very little if any is polymerized. The hydrocyanic acidpolymer is soluble in alkaline solutions and a very small percentagewill discolor the solution to a very considerable extent.

From the foregoing it appears that I have produced as a new product,calcium cyanide in a substantially pure and solid form and I havedevised a simple and relatively inexpensive process for the manufactureof this product. While I prefer to prepare the ammonia-containingcyanide from which the ammonia is removed by the process of my copendingapplication I can, of course, produce the normal calcium cyanide byremoving ammonia from ammonia-containing'cyanide prepared in anysuitable way. The invention is based, therefore, upon the discovery thatthe ammonia-containing cyanide can be freed from combined ammoniawithout decomposition of the cyanide.

Various changes may be made in the de tails of operation of the processand in the apparatus employed in connection therewith Without departingfrom the invention or sacrificing any of the advantages threof.

I claim 1. The product comprising a. compound in a dry and solid statehaving a composition corresponding substantially to the formula Ca(CN)2. The product comprisin a compound in a dry and solid state having acomposition corresponding substantially to the formula Ca(CN) and beingslightly basic.

3. The product comprising a compound in a dry and solid state having acomposition corresponding substantially to the formula C I(CN)2 andcontaining traces of ammonia.

In testimony whereof I affix my signature.

ROBERT W. POINDEXTER, JR.

